1. Filed of the Invention
The present invention relates generally to a finder equipped with an indicator, and more specifically to an indicator-within-finder comprising an optical member such as hologram, which is used with cameras such as silver-salt cameras or digital still cameras.
2. Discussion of Related Art
So far, many proposals have been made of finder indicators used with cameras, which are generally broken down into (a) a type of for guiding information from outside an optical path using a microprism, (b) a type for providing information to a user by emitting light from a light source from the side of an eyepiece system, (c) a type having a liquid crystal display device located within an optical path, and (d) a so-called illuminated type where indication systems constructed apart from a finder visual field system are placed one upon another by a half-silvered prism or half-silvered mirror. With type (a) often used with single-lens reflex cameras, high-quality indications are obtainable, but the indications are limited to small sizes and presented on the periphery of the visual field as well. Type (b), often used with compact cameras, is inexpensive because of the simple design of emitting light from a light source, but is inferior in terms of the quality of indications.
In type (c) which has been used with recently developed compact cameras, a liquid crystal display device is located at an intermediate image plane position in a finder system, so that indications can be obtained at a desired position in a visual field by changing an indication pattern at a user's disposal. Accordingly, this type of indicator has a very high degree of flexibility and so is capable of indicating more and more information. However, one problem is that the finder becomes dark due to the low transmittance of currently available liquid crystal display devices. Another problem is that the finder is colored due to the hues or tints inherent in liquid crystals. Type (d) is an old-style finder used with traditional cameras but has been reused in recent years. In particular, a combination type (d) and type (c) indicator has often been noticeable. In a camera where this type is combined with an Albada finder, very satisfactory indications are obtainable because flares peculiar to the Albada finder are much reduced. In principle, indications are obtainable at a desired position in the finder visual field. Although this type indicator has a high degree of flexibility, it is unfavorable for size and cost reductions because the indication optical system and the visual field optical system are of equal size.
On the other hand, an indicator using a hologram has recently been proposed in the art, as typically disclosed in JP-A's 9-15684, 9-80589 and 9-127457. JP-A 9-15684 shows one application of such an indicator to an Albada finder, wherein a hologram previously obtained by multiple recording is bonded to one surface of an eyepiece so that an indication recorded therein can be reconstructed by illumination with a reconstructing light source. Since the hologram usually has a plurality of indications recorded therein, reconstructing light sources corresponding to desired indications may be interchanged for illumination purposes.
On the other hand, JP-A 9-127457 shows an indicator used with a vehicle, wherein a hologram is incorporated in a front glass to provide a driver with information regarding speed, etc. The absolute size of this indicator is much larger than that of an indicator used in a camera finder, and has a large available space and is of simple construction. JP-A 9-127457 teaches a turn-back structure so as to reduce the distance of the hologram to an indication portion.
In the above prior art, the indicators may be constructed with no difficulty because there is a space for accommodating holograms. In a real image type finder used with a camera, however, there is no space for receiving a hologram because of the need for an image erection system for image inversion.
In the prior applications of holograms to finders, the holograms are of the recorded type and so have a limited degree of flexibility in indications. In addition, a plurality of interchanging light sources or some movable mechanisms are required. Thus, the prior art device have grave demerits.